Enhanced spontaneous metastasis of mouse carcinoma cells transfected with an activated c-Ha-ras-1 gene

Clonal changes in tumours during growth and progression evaluated by southern gel analysis of random integrations of foreign DNA

We have exploited random integrations of foreign DNA as a means of genetically tagging tumour cell populations with which to analyse the clonal evolution of tumour growth in vivo. Transfection of a non-metastatic mouse mammary carcinoma called SP1 (or a metastatic variant, SP1HU9L) with the pSV2neo plasmid or retrovirus vector infection with a "clipped-wing' vector (delta p delta eMoTN) was used to generate large numbers of uniquely marked tumour cell clones in single-step selections. The basic approach was to pool large numbers of independently marked transfectants or infectants, inject these cells into mice and analyse the resulting primary tumours and/or metastases later. Overgrowth or derivation of tumour masses by a limited number of clones could be detected by Southern gel analysis. The main findings were: (i) injection of pooled populations containing large numbers of uniquely marked cell clones (up to several thousand) invariably resulted in advanced primary tumours that contained a very limited number of clones, and in some cases only one easily detectable clone; (ii) primary tumours could be overgrown within six weeks by the progeny of the same single metastatic clone when the inoculum contained 1-10% metastatic cells, which suggests that metastatic SP1 cells have a selective growth advantage in primary tumours as well as for metastatic spread; and (iii) spontaneous lung metastases were clonal or biclonal at the time of analysis. The results show that spontaneous metastases can develop from a genetically distinct subpopulation of cells in a non-random (i.e. selective) manner. Because primary tumours can become overgrown by the progeny of a metastatic clone, results of any comparison of the properties of a primary tumour with a distant metastasis could be affected by the stage at which the primary tumour is removed and analysed.

Oncogene induction of metastases

A metastatic colony is the end result of a complex series of steps involving multiple gene products. In some cases, the augmented metastatic potential of certain tumour cells may be due to the increased expression of specific gene products which confer a selective advantage. Transfection of the c-Ha-ras oncogene into suitable recipient cells constitutes a powerful experimental model with which to identify putative gene products augmented in highly metastatic tumour cells compared to their non-metastatic counterparts. Transfection of the activated ras oncogene into 3T3 and 10T1/2 embryo fibroblasts, and adult rat fibroblasts, results in transformants which produce high numbers of spontaneous metastases in nude mice or syngeneic recipients. The ras oncogene will also increase the metastatic aggressiveness of murine tumours with low metastatic potential. However, the ras oncogene will not induce the metastatic phenotype in all recipient cells. Furthermore, specific genes such as adenovirus 2 E1A suppress the ability of ras to induce the metastatic phenotype. Natural 'suppressor' gene products may exist which render certain cells resistant to the induction of metastases by ras. Ras oncogene transfection induces the production of type IV collagenase, motility factors and growth factors. The ras oncogene therefore induces a cascade of gene functions leading to rapid progression to the metastatic phenotype. The mechanism of the induction probably involves complex interactions between the ras p21 product and multiple cellular gene products.

H-ras and Nm23-H1 gene expression and proteolytic activity in squamous cell carcinoma of the uterine cervix

BACKGROUND

The invasive and metastatic potential of malignant cells results from complex interactions of numerous factors not yet fully understood. Genomic alterations such as ras overexpression and nm23-H1 inhibition have been found to be frequently associated with increased invasiveness in various cancers. On the other hand, secretion of different proteinases are necessary for malignant cells to traverse a network of matrix macromolecules, but the relationship between the genomic alterations and the proteolytic phenotype is still unclear. Our aim was to investigate whether the appearance of the proteolytic phenotype had any correlation with the expression of H-ras and nm23-H1 genes in carcinoma of the uterine cervix.

METHODS

Twenty-five samples from patients with carcinoma of the uterine cervix at different clinical stages were studied. Cathepsin B1, plasminogen activator, and collagenase activity were assessed in tissue cytosols using specific synthetic oligopeptides as substrates. The expression of H-ras and nm23-H1 was investigated by means of immunohistochemistry and in situ hybridization.

RESULTS

Our results showed that cathepsin B1 was the most consistently elevated proteinase, demonstrating a linear correlation with clinical staging. H-ras expression was found elevated in 40% of the cases. Nm23-H1 protein immunoreactivity was positive in 40% of the cases. No correlation was found among H-ras, cathepsin B1 activity, and survival rate. Among cases with high cysteine proteinase activity, a different clinical behavior depending on the expression of Nm23-H1 was observed. The cases with Nm23-H1 protein had a markedly better survival rate than those lacking this protein. In contrast, the absence of Nm23-H1 in association with high cathepsin B1 activity was a clear indicator of a poor prognosis.

CONCLUSIONS

These findings suggest a complex interaction between the proteolytic phenotype and the expression of H-ras and nm23-H1 genes in carcinoma of the cervix that influences the clinical behavior of the tumor.

Transferrin receptor overexpression enhances transferrin responsiveness and the metastatic growth of a rat mammary adenocarcinoma cell line

We previously found that breast cancer cell transferrin receptor expression and proliferative response to transferrin often correlated with metastatic capability. To further explore this, we transfected mammary tumor cells with a cDNA coding for the transferrin receptor and examined the effects of its overexpression on various cellular properties. A human transferrin receptor expression plasmid was made by excising the cDNA for the receptor from pcDTR1 and ligating it into the multiple cloning site of pcDNAINeo. The resulting construct was transfected into the poorly metastatic rat MTLn2 line that expresses low endogenous levels of rat transferrin receptor, and transfection-induced receptor expression was ascertained using antibodies specific for the human protein. Approximately 50% of the initial geneticin-resistant transfected MTLn2 cells overexpressed human transferrin receptor protein. High expressors were further isolated by four sequential FACS sorts. The final cell population expressed approximately 3-7 times more cell surface transferrin receptor than did vector transfected controls. Both lines proliferated at the same rate in normal (medium plus 5% FBS) culture conditions. However, in serum-free conditions, the transferrin receptor overexpressor cells displayed a pronounced proliferative response to transferrin whereas the control line did not. When injected into the mammary fat pads of female nude mice, cells from both lines formed micrometastases to the lung that were specifically visualized by immunohistochemical staining of rat cytokeratin 17. This revealed that the transferrin receptor transfected line formed larger lesions of this nature than did cells from the vector transfected controls. When injected into the tail vein of female nude mice, the transferrin receptor overexpressors likewise formed gross lung metastases of remarkably greater size than did the vector only transfectants. Overexpression of cell surface human transferrin receptor on MTLn2 cells appeared to affect their in vitro growth response to transferrin and their ability to grow at a secondary site in vivo.

Generation of metastatic variants by transfection of a rat non-metastatic epithelial cell line with genomic DNA from rat prostatic carcinoma cells

Prostate cancer is the second leading cause of male death from malignant disease in Europe and in the USA. Failure to prevent or eliminate metastatic dissemination is a fundamental problem underlying the current inadequate treatment of prostate cancer, and novel therapeutic strategies are required if this disease is to be successfully managed. No independent markers are yet available to predict the behaviour of any individual prostate cancer, particularly its potential to metastasize, and there is now an urgent prerequisite to identify and characterize genes specifically involved in determining the metastatic phenotype of prostate cancer cells before any biologically appropriate treatment modality can be devised. To identify DNA sequences that trophically promote the metastatic phenotype, we have established a new transfection assay with which to monitor activity of prostate cancer genomic DNA. Rat prostatic G and AT6.1 cell lines derived from the same original Dunning R3327 rat prostatic carcinoma exhibit, respectively, low- and high-metastatic phenotypes when grown in syngeneic Copenhagen rats. Rat mammary epithelial cell line 'Rama 37' derived originally from Wistar-Furth rats yields benign non-metastasizing adenomas when inoculated subcutaneously into syngeneic animals. In this report, the Rama 37 cell line is successfully used as the recipient cell-line for transfected DNA fragments extracted from rat prostatic carcinoma G and AT6.1 cells. New metastatic variants of Rama 37 cells have been generated. Enzymatically fragmented genomic DNA from rat metastatic prostate carcinoma cell lines was co-transfected together with plasmid pSV2neo into parental Rama 37 cells, followed by culture in the presence of Geneticin-G418 to select for the transfected cells. To enable subsequent identification of metastasis-promoting DNA sequences, the fragmented genomic DNA sequences were covalently attached to specifically engineered linker DNA molecules to flank the genomic DNA before transfection. Thereafter, the resulting transfectants were pooled and inoculated into mammary fat pads of female Wistar-Furth rats. Metastases produced by the transfectant cells in vivo were reestablished from secondary tumours and probed for the presence of the specific synthetic oligonucleotide sequences that flanked, and hence identified, the presence of the transfected DNA. These new metastatic cells are shown to provide a sensitive assay system with which to detect DNA sequences responsible for conveying the metastatic phenotype of prostate cancer when inoculated into syngeneic rats.

Degradation of endothelial cell matrix collagen is correlated with induction of stromelysin by an activated ras oncogene

A conditional expression system was established whereby the human K-ras, v-src, and v-mos genes were cloned into a conditional expression vector downstream of the dexamethasone-inducible mouse mammary tumor virus long terminal repeat. Rat-1 fibroblasts were transfected with these constructs and selected in medium containing G418. Cloned transfectants were isolated and characterized for absolute dependence on dexamethasone for expression of oncogene products and anchorage-independent growth in soft agar. Expression of activated p21K-ras(val12) enabled the fibroblasts to degrade extracellular matrix collagen secreted by murine microvessel endothelial cells. Concurrent with p21K-ras(val12) induction a proteinase with the characteristic size and substrate specificity of transin, the murine homologue of the human matrix metalloproteinase stromelysin, was expressed and secreted. Induction of v-mos and v-src oncogenes resulted in little or no detectable transin expression respectively coinciding with a relative or absolute failure to increase degradation of extracellular matrix collagen. This study suggests that in this system the expression of the ras oncogene can contribute to the in vitro invasive behavior of tumor cells by upregulating the production of a metalloproteinase capable of degrading collagen synthesized by vascular endothelial cells.

Acquisition and enhanced expression of the metastatic phenotype following transfections of genomic mouse tumor DNA containing human SCLC gene sequences

Previous primary and secondary co-transfections of genomic DNA from a metastatic human small cell lung cancer cell line into NIH/3T3 cells resulted in a murine fibrosarcoma cell line (Tx93B) that produced frequent spontaneous lung metastases in subcutaneously injected tumor-bearing nude mice. In order to transfer the acquired metastatic behavior to additional cell lines that could then be tested in syngeneic immunocompetent animals, DNA from Tx93B cells was transfected without additional neo gene into Balb/c embryo fibroblasts, which led to the isolation of a tertiary transfectant cell line (D3) of low spontaneous metastatic potential in normal Balb/c mice. Subsequent cell lines established serially from lung metastases in mice injected with D3, and metastatic descendants of D3 (all selected for the original neo marker in G-418), resulted in three generations of metastatically variant cell lines capable of causing pulmonary metastases in 11.1%, 54.6%, and 89.5%, respectively, of subcutaneously injected animals, and in 100% of normal mice injected intraperitoneally. There was no apparent ras-family oncogene participation in the metastatic behavior of either of the two DNA donor cell lines or in the metastatically variant tertiary transfectants. Gelatin zymography indicated that the secretion of gelatinolytic enzymes in vitro by the variant cell lines was inversely proportional to their metastatic capability. Human Alu repeat gene sequences detected in the metastatic variants suggested that co-transfected metastasis-associated genes present in the original human DNA donor cell may have contributed to acquisition of the metastatic phenotype by the tertiary transfectant cell lines. The increase in metastatic potential observed in successive generations of the D3-derived tumor cell lines, further suggested that selection for cells having increased metastatic capability had occurred during passage in vivo accounting for the phenotypic change. Because of their common origin and progressively metastatic nature these cell lines may prove useful in the identification of metastasis-associated genes accessible through the use of differential expression cloning strategies.

A radiation-induced murine ovarian granulosa cell tumor line: introduction of v-ras gene potentiates a high metastatic ability

A non-metastatic epithelial tumor cell line, OV3121, was established from ovarian granulosa cell tumor in B6C3F1 mouse irradiated with 60Co-gamma rays. OV3121 cells showed an epithelial morphology and grew in monolayer with a population doubling time of 28-30 h. The production of estradiol and the expression of cytokeratin confirmed the epithelial origin of the line. No pulmonary metastasis was observed from solid tumors after subcutaneous (s.c.) injection or after intravenous (i.v.) injection of a clonal subline, OV3121-1 cells. We examined the experimental metastasis of individual clones of OV3121-1 cells, containing various introduced viral oncogenes: v-Ha-ras, v-Ki-ras, v-fms, v-mos, v-raf, v-src, v-sis, v-fos and v-myc. Among them, only OV3121-1 cells with v-Ha-MuSV or v-Ki-MuSV produced lung colonies at high frequencies. In a more detailed analysis, the v-Ha-ras transfectants OV-ras4 and OV-ras7 were found to form colonies in various organs by metastasis from tumors after s.c. injection, as well as lung colonies after i.v. injection. Moderately metastatic OV-ras7 cells showed high gelatinolytic activity at 72 kDa (MMP-2) and 92 kDa (MMP-9) as compared with the parental OV3121-1 and OV-Neo control cells by zymographic analysis. However, more metastatic OV-ras4 cells produced progressively weaker bands of 72 kDa gelatinolytic activity. No gross alterations in the expression of MMP-1, MMP-3, TIMP-1 and TIMP-2 transcripts were detected in these cell lines. These results suggest that this ovarian granulosa cell tumor line may provide a useful system for understanding the mechanisms by which oncogenes influence the occurrence of metastasis.

Branching N-linked oligosaccharides in breast cancer

Tumor progression in rodent and human tumors is commonly associated with changes in glycoprotein glycosylation, in particular increased beta 1-6GlcNAc-branching, a regulatory step in expression of polylactosamine and extended-chain Lewis antigens. Loss of the branched oligosaccharides in murine tumor cells either due to somatic mutation, or treatment of the cells with the oligosaccharide processing inhibitor swainsonine, blocks tumor cells invasion in vitro and reduces solid tumor growth in vivo. Swainsonine and other inhibitors of N-linked oligosaccharide processing may be useful anti-cancer drugs, a premise which has begun to be tested in humans.

Transfection of metastatic capability with total genomic DNA from human and mouse metastatic tumour cell lines

From a large series of experiments involving transfer of high molecular weight total genomic DNA from highly metastatic human and mouse tumour cell lines to other mouse tumour cell lines we have derived a few cell lines with greatly augmented metastatic properties. In one of these experiments the transfected cell line (designated AH8 Test) not only colonised the lungs but also formed secondary tumour colonies in several extrapulmonary sites including the skin, skeletal muscles, bone, liver diaphragm, spleen and heart. There were no qualitative and quantitative effects of this magnitude when we used DNA from several non-metastatic or non-tumourigenic sources. Secondary transfection of metastatic capability with DNA obtained from a metastasis formed by one of the primary transfectant lines (AH8 Test) has also been accomplished. Concomitant transfer of human DNA through both transfection cycles in this experiment was confirmed by a variety of methods including Southern blot analysis, in situ hybridisation and polymerase chain reaction (PCR) amplification of DNA using primers recognising human-specific Alu repeat sequences. The findings offer opportunities for the isolation of sequences programming metastatic behaviour and we have cloned and sequenced a fragment of human DNA, which has not been previously characterised, from the transfected cells.

Persistence of Ha-ras-induced metastatic potential of SP1 mouse mammary tumors despite loss of the Ha-ras shuttle vector

Previous studies have shown that the SP1 mouse mammary adenocarcinoma cell line, which is tumorigenic but nonmetastatic, acquires metastatic potential when transfected with the activated human Ha-ras gene. In addition, the process of calcium phosphate-mediated DNA transfection, as well as treatment with the calcium ionophore A23187 or with phorbol 12-myristate 13-acetate, can also result in heritable changes in the malignant behavior of SP1 cells. It was of interest, therefore, to determine whether the metastatic consequences of Ha-ras oncogene expression in SP1 cells are a primary effect of the transfected gene or whether heritable secondary changes are induced by Ha-ras oncogene expression. In the latter case, continued expression of the Ha-ras oncogene would not be required to maintain the metastatic phenotype. To test this hypothesis we introduced the Ha-ras oncogene into SP1 cells on a shuttle vector in which maintenance of the vector was dependent on selection for resistance to the antibiotic G418. Subclones which had lost the transfected Ha-ras gene were subsequently isolated following growth in nonselective medium. The Ha-ras-transfected clones and the revertant subclones were found to be equally metastatic, indicating that transfection with the Ha-ras gene does induce stable secondary changes in the metastatic phenotype of SP1 cells.

Evolutionary somatic cell changes in cervical tumour progression quantitatively evaluated with morphological, histochemical and kinetic parameters

The somatic cell changes which characterise malignancy evolution in human cervical preneoplastic and neoplastic lesions have been assessed on histological sections by means of a computerised image analyser. Many features have been simultaneously measured on each cell of the lesions studied, and the following results have been obtained: Some features, mainly kinetic, show continuously increasing values which express changes correlated to the increasing malignancy; other features, especially related to nuclear atypia, cellular heterogeneity and the degree of aneuploidy, have values dropping at the level of early stromal infiltration, which can be morphometrically characterised as composed of relatively homogeneous phenotypes; these features seem to express the degree of genetic instability and relate to the evolutionary somatic cell changes; tumour progression evolves through sequential discontinuous steps, each of them characterised by specific phenotypical features of the neoplastic cell population; the neoplastic cells in the foci of early stromal infiltration and vascular invasion, phenotypically more homogeneous than the parent cell populations of carcinoma in situ and infiltrating carcinoma, seem to possess a greater genetic stability.

Experimental metastasis of oncogene-transformed NIH 3T3 cells in chick embryo

By means of a highly sensitive and quantitative assay for specific detection of metastasized tumor cells in chick embryonic organs using the polymerase chain reaction (PCR), we have examined the experimental metastatic ability of individual clones of NIH 3T3 cells, transformed with oncogenes: v-Ki-ras, v-Ha-ras, v-src, v-fos, and v-abl. Such a transformed clone had different metastatic abilities in different embryonic organs. Among them, two clones of NIH 3T3 cells transformed with ras-oncogenes (v-Ki-ras or v-Ha-ras) metastasized to liver and lungs of chick embryo, and grew there more rapidly than the other clones. The parental NIH 3T3 cells were detected as slight bands of PCR products after iv injection, indicating some cells were trapped in chick embryonic organs, but did not grow. These findings indicate that the transformed cells are able to invade the organ tissues and grow in embryonic chick organs, but non-metastatic cells such as the untransformed-NIH 3T3 cells are not able to grow in the secondary sites. These experiments clearly demonstrate the usefulness of this assay system to study genes involved in malignant transformation.

Spontaneous metastatic potential of rat hepatocarcinoma cells after cell fusion or DNA transfection

Eight LF x ICIG cell hybrid clones, isolated upon fusion of normal ICIG-7 human fibroblasts with tumorigenic, non-metastatic LF Cl.2A cells derived from a DAB-induced rat hepatocarcinoma, were studied. They were all highly tumorigenic and were capable of developing spontaneous lung metastases in syngeneic animals. All the hybrids were characterized by a rapid loss of human chromosomes. However, in long-term culture, they all revealed a persistence of human genetic information as assessed by Southern blotting. In hybrid lines in which human chromosomes were still visible, the most recurrent were numbers 7 and 9. Neither chromosome 7, previously reported to bear some of the genes controlling metastasis in human X mouse T-cell hybrids, nor chromosome 9 appeared to be correlated with the metastatic potential of LF X ICIG hybrids. The same conclusion applied (1) to a human 3.3-kb EcoRI DNA fragment which was amplified (approx. 10-fold) only in metastases induced by one out of 3 metastatic hybrids tested; (2) to the transcription level of c-Ha-ras and c-Ki-ras genes which was enhanced (approx. 4-fold) in metastatic and non-metastatic lines as well. Co-transfection of LF Cl.2A cells with pHSG 272 selectable marker DNA and genomic DNA from normal ICIG-7 human cells or from a hybrid-induced metastasis, reproducibly gave rise to geneticin-resistant transfectants capable of producing spontaneous lung metastases. Neither transfectants nor transfectant-induced metastases harbored detectable human DNA sequences but all harbored pHSG 272 DNA. These results again call for caution in gene transfer studies of the metastatic process.

Cytokinesis is more rapid in Ha-T24-ras transfected rat embryo fibroblasts than in non-transfected control cells

It has long been known that neoplastic cells are characterized by increases in cell motility. Earlier studies from this laboratory indicated that mitotic events were also altered in many tumor and experimentally transformed cells and that this included increases in metaphase duration and a reduction in the duration of cytokinesis. The studies presented in this paper were done to determine whether or not transfection of normal rat embryo fibroblasts by the Ha-T24-ras oncogene could also produce such alterations in mitotic events. The results obtained with the use of time lapse video microscopy indicate that neither the duration of metaphase nor the rate of chromosome movement during anaphase was altered but that the rate of furrow progression during cytokinesis occurred at a significantly more rapid rate. Thus, the cellular alterations induced by transfection with Ha-T24-ras accelerate microfilament-dependent cytokinetic furrowing without significant effects on microtubule-dependent mitotic events. One of several possible mechanisms that could account for these observations involves a down regulation of protein kinase C which has been reported to occur in many neoplastic cells including those transformed by ras. Such a hypothesis could also have broader implications because it may be applicable to the increase in motility and metastatic activity generally observed in transformed cells.

Maintenance of liver function in long term culture of hepatocytes following in vitro or in vivo Ha-rasEJ transfection

Collagenase isolated rat hepatocytes were transfected with liposome encapsulated pEJ (LE-pEJ), a plasmid carrying the human cellular activated Ha-rasEJ oncogene. A proliferative cell line was cloned from these cells transfected in vitro. It secreted per day 0.87 micrograms albumin and 0.32 microgram transferrin per 10(6) cells, and 11.06 nmol free and conjugated bile acids (BA) per mg protein. Also, it metabolized 2-acetylaminofluorene (2-AAF) into N- and ring-hydroxylated metabolites and 2-aminofluorene at rates of 1.50, 9.73, and 1.98 nmol/mg cell protein/24 hr, respectively. Rats were i.v. injected with both LE-pEJ and LE-p17hGHneo carrying the hGH cDNA gene, and secreted hGH in the plasma which induced the synthesis of anti-hGH antibodies. A cell line was cloned from cultures of primary hepatocytes isolated from the liver of transfected rats. After 2 to 3 months in culture, this cell line secreted per day 18.9 micrograms albumin and 11.0 micrograms transferrin per 10(6) cells, 38.75 nmol total BA per mg cell protein, and up to 31 ng hGH per 10(6) cells without cloning hGH recombinant cells. A 24 hr control culture of primary hepatocytes isolated from non transfected rats secreted 25.5 micrograms albumin and 11.7 micrograms transferrin per 10(6) cells, and produced 21.64 nmol total BA and 2.13 nmol N-OH-2-AAF per mg cell protein. Hence, Ha-rasEJ transfection of either hepatocytes in vitro or liver cells in vivo, initiated cell cycles leading to presumptive proliferating hepatocytes which express liver function.

New insights into the causes of cancer

Recent advances in molecular biologic analysis have led to major new insights concerning the genetic mechanisms underlying the development of cancer. This article examines the current state of our understanding of the genetic basis underlying the possible mechanisms of carcinogenesis and metastasis. The nature of the genetic lesions found in some cancer-causing genes, cancer-inhibiting genes, growth factor genes, and metastasis genes is discussed, as is the impact that these may have on clinical oncology.

Ras levels and metalloproteinase activity in normal versus neoplastic rat mammary tissues

We have previously reported that activated ras oncogenes can simultaneously switch on the metastatic phenotype and increased capability to degrade type IV collagen. Here the relationship between c-H-ras, metalloproteinase expression and metastatic behavior was studied in N-nitrosomethylurea (NMU)-induced rat mammary carcinomas, which are known to possess activated c-H-ras. When comparing normal rat breast tissue to mammary carcinomas there was no direct relationship between ras DNA levels and neoplastic changes. Furthermore, there were no consistent differences between metastatic and non-metastatic carcinomas, or between primary tumors and metastases. The NMU-induced rat mammary carcinomas expressed two major gelatinolytic metalloproteinases (gelatinases) of 65 and 92 kD, but only the 65 kD gelatinase was detected in normal breast tissue and a rat fibroma. Type IV collagenolytic activity per 5 micrograms of protein was two to three times higher in the mammary carcinomas than in the normal breasts, whereas the primary tumors did not differ from the corresponding metastases. This study shows that ras amplification is not necessary for development of the malignant or metastatic phenotype in the NMU-induced rat mammary carcinoma model. We have also found that induction of p21 ras protein synthesis in a v-H-ras transfected NIH/3T3 (433) cell line, containing a glucocorticoid promoter, does not lead to an increase in metastatic capacity.

Transfection of a non-metastatic diploid rat mammary epithelial cell line with the oncogenes for EJ-ras-1 and polyoma large T antigen

Transfection of rat mammary (Rama) 37 epithelial cells which yield non-metastasizing adenomas in syngeneic Wistar-Furth rats with a drug resistance plasmid containing both the neo gene and EJ-ras-1 (pSV2neo.ras) or with pSV2neo and a plasmid encoding the large T Antigen (pLT214) of polyoma virus yields drug-resistant transformants with a frequency of 10(-5). Representative transformants have been propagated in neo-selecting medium to yield various cell lines. The 7 lines transfected with pSV2neo.ras (EJ1 set) and the 10 lines co-transfected with pSV2neo and pLT214 (LT1 set) all produce tumours at subcutaneous (s.c.) sites with a shorter median latent period than tumours produced by the parental Rama 37 cells. In addition, the LT1 set of transformants yields a higher incidence of tumours than the Rama 37 cells. No metastases are produced when any of the oncogene transformants are inoculated s.c. into rats. However, when an EJ1 representative is inoculated intravenously (i.v.), tumour deposits are found in the lungs of the host animals. In contrast, other Rama 37 variants that metastasize from s.c. sites fail to produce any metastases when inoculated i.v. The oncogene transfectants contain integrated DNA that hybridizes to neo and to the requisite oncogenic DNAs; the pattern of hybridizing bands to the transfected genes and their expression as mRNA is complex, and is presented in detail.

Hormone sensitivity in vitro and in vivo of v-ras-transfected MCF-7 cell derivatives

Human mammary carcinoma cell lines (MCF-7) were analysed for their hormone sensitivity before and after transfection with a v-Ha-ras oncogene or with a neomycin-resistance gene followed by selection in vitro or in vivo. Our aim was to test how the expression of the ras oncogene would influence the estradiol sensitivity of MCF-7 cells. In culture, MCF-7 cells expressing the viral p21 oncogene product, as compared to parental MCF-7 cells and their control derivatives, showed lower levels of a 67-kDa estrogen receptor. Progesterone receptors, however, remained sensitive to up-regulation by estrogens. The oncogene-expressing cells were less sensitive than all controls to stimulation of proliferation by 10(-8)M estradiol or to inhibition of proliferation by 2-CH3-4-OH tamoxifen, and this was not dependent upon the type of culture medium used. After s.c. or i.p. injection into female athymic nude mice, ovariectomized or left intact, the growth of MCF-7 cells expressing the ras oncogene product and of all control cells was sensitive to stimulation by estrogen supplementation. Conversely, cell lines derived from tumors generated with long latency in untreated athymic nude mice by v-ras-expressing MCF-7 cells showed efficient formation of quickly growing tumors in the absence of estrogen supplementation. No differences were observed in invasion and metastasis of the different MCF-7 cell types injected into athymic nude mice that were supplemented with estrogens or not.

A positive association between agonist-induced cyclic AMP production in vitro and metastatic potential in murine B16 melanoma and hamster fibrosarcoma

A positive association between agonist-stimulated cyclic AMP production in vitro and both experimentally induced (B16 melanoma) and spontaneous (fibrosarcoma) metastases were found. Five B16 melanoma cell lines producing varying degrees of lung colonization following intravenous injection and three hamster fibrosarcoma cell lines producing a varying number of metastases in lungs and regional lymph nodes after removal of the primary tumour were studied. Agonist-stimulated (forskolin and melanocyte-stimulating hormone), but not basal cyclic AMP accumulation, increased with increasing metastatic potential. This relationship did not extend to other intracellular signalling systems as determined by investigation of basal or foetal-calf stimulated phosphatidylinositol hydrolysis for either tumour type. Intracellular free calcium was also similar in B16 melanoma cell lines of varying metastatic potential.

ras transfection and expression does not induce progression from tumorigenicity to metastatic ability in mouse LTA cells

Studies testing the ability of a transfected ras oncogene to confer metastatic properties on non-metastatic cells have yielded conflicting results. Most of these studies have used recipient cells at early stages of progression (primary or immortalized, non-tumorigenic lines). In this study we tested the ability of the T24-H-ras oncogene to induce progression of tumorigenic, non-metastatic, murine LTA cells to a metastatic phenotype. Metastatic ability was assessed in complementary assays in two immune-deficient hosts, nude mice (after s.c. injection) and chick embryos (after i.v. injection), to determine if ras transfection affected metastatic properties in hosts lacking an intact immune system. Even with greatly elevated levels of ras p21 protein, pools of ras-transfected cells as well as individual clonal populations remained non-metastatic in both hosts. Serial in vivo passaging did not consistently enhance for either ras expression or metastatic ability. We conclude that expression of an activated ras oncogene in LTA cells does not induce progression from a tumorigenic to a metastatic phenotype. These results are in marked contrast to those obtained for ras expression in most other types. High levels of expression of an activated ras oncogene thus do not always promote progression from tumorigenicity to metastatic ability.

Cell-matrix interactions during tumor invasion

This manuscript reviews the molecular aspects of tumor cell invasion of extracellular matrix. The changes in cell:substrate and cell:cell receptors that characterize motile cells are discussed for their importance not only in mediating invasive cell behavior, but also as diagnostic markers for invasive potential. Autocrine motility and scatter factors probably have key roles in initiating migratory behavior, while specific and non-specific extracellular matrix alterations can facilitate cell locomotion. The manuscript reviews reported changes, such as induction of cell motility, matrix degrading enzymes, and invasive/metastatic potential, which can follow transfection with ras oncogenes, and details the key roles of metalloproteinases, heparanase, and plasminogen activator in matrix degradation. Enzymatic inhibitors of initial steps in extracellular matrix degradation, such as rTIMP, and synthetic blockers of adhesive steps in tumor cell invasion represent types of reagent with potential as anti-metastatic agents. Their potential usefulness may be increased if they can be incorporated into a novel, long-term, non-traditional delivery system.

Neoplastic transformation of a human kidney epithelial cell line transfected with v-Ha-ras oncogene

We have recently shown that normal human kidney epithelial (NHKE) cells were immortalized by treatment with Ni(II) alone. In the present study the immortalized human kidney cell line (IHKE) was transfected with a plasmid construct containing the v-Ha-ras oncogene (pZipras). After transfection, the cell lines formed tumors in athymic nude mice, whereas the ZipNeoSV(X)-transfected IHKE control cultures formed no tumors. Tumor cell lines (THKE) were established from the tumors in nude mice. These cells appear to be of human epithelial origin and express high levels of Ha-ras transcript. Karyotypic analysis was performed. The cell lines were tri-, tetra- or pentaploid. A consistent finding in the IHKE, IHKZE and THKE cells was increased numbers of chromosomes 17 and 7p+. Some marker chromosomes were identical in the IHKE and THKE cell lines, underlining their common origin and their possible importance in the carcinogenic process. This shows that the combined action of a chemical carcinogen [i.e., Ni(II)] and v-Ha-ras oncogene resulted in fully transformed human kidney epithelial cells, consistent with a step-wise progression of human epithelial cell transformation.

Molecular oncogenetics of metastasis

Metastasis is a complex non-stochastic process that is most likely the result of genetic and epigenetic interactions of a wide variety of genes. The search for a single gene which can encompass such a pleiotropic response as to account for the observed phenotypic characteristics of metastatic tumour populations has been unsuccessful. Particular studies involving gene transfection, subtractive hybridisation and cell fusion are beginning to identify specific genes which contribute to metastasis in some cell types. However, such analyses are complicated by the inherent genetic instability and phenotypic heterogeneity present in tumour populations. A more detailed understanding of the metastatic process may require an abandoning of current generalised approaches to metastasis in favour of concentrating on key components of the metastatic cascade such as adhesion and invasion.

The ras oncogene and tumour metastasis: observations on murine cells transfected with activated human c-Ha-ras

Transfection of cells with cloned genes or total genomic DNA offers a means for studying aspects of neoplastic behaviour. We have used this method to examine whether incorporation of the cloned 6.6-kilobase (kb) fragment of DNA containing the mutant c-Ha-ras human oncogene can confer metastatic capability on murine NIH 3T3 cells. Cells co-transfected with the mutated ras gene and the neomycin resistance marker pSV2neo were selected by culture in neomycin. On subcutaneous inoculation into MF 1 nude mice, these cells proved to be tumourigenic with short latent periods (approximately 14 days)--nude mice were used to circumvent immunological rejection of the mouse cells expressing the product of the human oncogene. Transfectants were capable of lung colonisation after intravenous injection, but there was no evidence of spontaneous metastasis at autopsy, or on histological examination of the lungs and other organs, 90 days after inoculation. Incorporation of the transfected oncogene was confirmed by Southern blotting and its expression by dot-blot hybridisation and immunoprecipitation. The results in this experimental system indicate that transfection of a mutated human ras oncogene into non-neoplastic 3T3 cells can confer part of the metastatic phenotype, namely lung colonisation, but is not by itself sufficient to induce spontaneous metastatic behaviour.

Transformed NIH 3T3 cells expressing human melanoma N-ras oncogene metastasize to lymph node in nude mice

The effect of the N-ras oncogene on the propensity of transformed cells to disseminate from the tumor and to metastasize, using NIH 3T3 cells transformed either with human melanoma DNA containing the N-ras oncogene or with the cloned N-ras from human neuroblastoma, was investigated. The results show that NIH 3T3 expressing these genes readily formed tumors after subcutaneous injection in nude mice. Spontaneous lymph node metastasis was observed after a first cycle of transfection in one animal inoculated with cells containing human melanoma N-ras oncogene, and in 95 per cent of the animals after the second and third rounds of transfection, indicating that the metastatic capacity was transferred. In all cases human N-ras oncogene was found in both the metastases and the associated tumors. No control NIH 3T3 cells formed tumors or metastases in nude mice, and NIH 3T3 cells transfected with cloned N-ras activated oncogene formed tumors in 100 per cent of injected mice, but no spontaneous metastases. Thus human activated N-ras gene may not be sufficient to confer metastatic behavior in nude mice and the metastatic ability of human melanoma DNA transfected cells may be due to, among other possibilities, expression of other gene sequences from melanoma DNA co-transfected with the N-ras oncogene, or to specific activated murine sequences switched on during the initial process of transfection.

Isolation and characterization of a gene specifically expressed in different metastatic cells and whose deduced gene product has a high degree of homology to a Ca2+-binding protein family

The gene mts1, which is expressed specifically in metastatic cells, was isolated by molecular cloning coupled with differential DNA reassociation. Transcription of mts1 was found not only in tumor cells, but also in normal cells; homologous RNA was detected only in spleen, thymus, bone marrow, and blood lymphocytes. DNA sequencing of mts1 revealed an open reading frame containing information for a peptide of 101 amino acids, and the amino acid sequence suggested that the mts1 protein was identical to the previously isolated Ca2+-binding mouse protein (Jackson-Grusby et al. 1987; Goto et al. 1988). Thus, the mts1 protein is a member of the calcium-modulated protein family, and our data indicate that mts1 is involved in regulating the metastatic behavior of tumor cells.

Correlation between Ha-ras gene amplification and spontaneous metastasis in NIH 3T3 cells transfected with genomic DNA from human skin cancers

Our previous studies have shown that DNA from some human skin cancers contained activated Ha-ras oncogenes capable of inducing tumorigenic transformation when introduced into NIH 3T3 cells by DNA-mediated gene transfer. In addition, we found that NIH 3T3 cells transfected with DNA from one of the human skin cancers not only induced s.c. tumors at the site of injection but also metastasized spontaneously to the lungs in 100 per cent of nude mice injected. In this present study we examined the relationship between Ha-ras oncogene amplification and metastatic potential in tumors induced by various human skin cancer DNA-transfectants. Total cellular RNA was extracted from nude mouse tumor cell lines and analyzed by northern blot hybridization to a 32P-labeled, nick-translated Ha-ras probe. The metastatic potential of nude mouse tumor cell lines was assessed by their ability to form lung colonies after i.v. or s.c. injection. It was found that only the tumors expressing high levels of Ha-ras gene transcripts induced spontaneous metastasis after s.c. injection. There appeared to be little correlation between the level of Ha-ras oncogene amplification and experimental metastasis. These results suggest that amplification and overexpression of Ha-ras oncogene may play a role in the escape of cells from the primary tumor rather than in the ability of cells to survive in the circulatory system and colonize secondary sites.

Induction of the metastatic phenotype by transfection of the nuclear oncogene p53: increases in cytoplasmic diacylglycerol levels and reduction in class I major histocompatibility antigen expression are not sufficient to explain the changes in metastatic capacities

Transfection of the oncogene encoding the nuclear protein p53 into a low-metastatic mouse carcinoma cell line resulted in enhanced metastatic capabilities in clones that showed increased p53 protein expression [Pohl J, Goldfinger N, Radler-Pohl A, Rotter V, Schirrmacher V (1988) Mol Cell Biol 8:2078-2081]. This effect seemed neither to be due to increase in cytoplasmic diacylglycerol levels nor to reduced cell-surface expression of class I major histocompatibility antigens.

Expression of a transfected v-Harvey-ras oncogene in a Dunning rat prostate adenocarcinoma and the development of high metastatic ability

To investigate the role of oncogenes in the development of metastatic ability by prostatic cancer, the viral-Harvey-ras (v-H-ras) oncogene was introduced into the Dunning rat prostate adenocarcinoma cell line, AT2.1 by means of DNA transfection. The AT2.1 cell line is a cloned cell line that is anaplastic, rapidly growing, and has low metastatic potential; after subcutaneous (s.c.) inoculation in syngeneic rats, fewer than 10% of inoculated rats develop distant metastases. Calcium phosphate mediated DNA transfections of AT2.1 cells were performed with the v-H-ras oncogene or with control DNA. The in vitro growth rate of cloned transfectants, which contain and express the v-H-ras oncogene is similar to that of untransfected AT2.1 cells and of control transfectants. After s.c. inoculation in syngeneic rats, all transfectants produced rapidly growing tumors with similar growth rates. While control transfectants had low metastatic ability comparable to untransfected AT2.1 cells, the H-ras expressing transfectants metastasized in over 80% of inoculated rats. While the mechanism by which nonmetastatic Dunning tumor sublines spontaneously develop high metastatic ability in vivo during serial s.c. passage has not been addressed in the present studies, these studies do demonstrate that expression of an activated H-ras oncogene can reproducibly convert a tumorigenic nonmetastatic prostatic cell line to a highly metastatic state.

A model to account for the effects of oncogenes, TPA, and retinoic acid on the regulation of genes involved in metastasis

We have postulated that signals from the microenvironment can induce shifts in tumor cell phenotypes and that microenvironmental factors are therefore important for cancer metastasis. In this article we expand on this hypothesis and propose a model to explain (a) how extracellular signals can lead to changes in tumor phenotypes, and (b) how cytoplasmic oncogenes, which influence signal transducing pathways as well as nuclear oncogenes regulating gene expression via DNA binding transacting factors, might affect metastatic competence.

Detection of ras oncogenes by analysis of p21 proteins in human tumor cell lines

To detect mutationally activated ras oncogenes, we analyzed electrophoretic mobilities of ras p21 proteins utilizing the fact that many ras oncogenes produce abnormal p21 proteins that migrate at SDS/polyacrylamide gel electrophoresis as a fast-moving or slow-moving species in comparison to a normal p21 depending on the kind of mutation. Of 18 human tumor cell lines analyzed, four (SW480, SW620 and SW403 colon cancers, and SW626 ovary cancer) produced p21 belonging to the slow-moving species, suggesting a point mutation within codon 12 of a member of the three ras genes, H-, Ki- and N-ras. Subsequent DNA transfection analysis using NIH/3T3 cells as recipients identified activated Ki-ras oncogenes in the same four but not in other 14 cell lines. Thus, the analysis of p21 might serve as a rapid primary method to screen a large number of tumor materials for the presence of certain types of mutationally activated ras oncogenes.

Analysis of metastatic competence of mouse bladder carcinoma cells after transfection with activated Ha-ras or N-ras oncogenes

Transfection of the Ha-ras oncogene into a low metastatic epithelial cell line resulted in the acquirement of significantly increased metastatic capacity. This alteration in metastatic competence of a carcinoma line in a syngeneic system seemed to be a selective change and was not affected by parameters such as tumor latency period or local tumor growth. Transfection of the selection marker vectors with normal cellular DNA or with the N-ras gene did not lead to significantly increased metastatic capacity. Analysis of metastatic variants after oncogene transfection and in vivo selection showed integration of N-ras, but not of Ha-ras oncogenes. A possible role for the Ha-ras oncogene in the initial steps of metastasis will be discussed.

p53 increases experimental metastatic capacity of murine carcinoma cells

Transfection of a cloned p53 gene into a murine bladder carcinoma cell with a low metastatic capacity led to elevated levels of p53 protein in clonal transfectants. After intravenous inoculation into syngeneic mice, p53-transfected clones showed significantly increased metastatic potential in comparison with control transfectants. The observed change did not seem to be due to a change in growth potential per se since the cell lines showed similar growth properties in vitro.

Selective enhancement of metastatic capacity in mouse bladder carcinoma cells after transfection with DNA from liver metastases of human colon carcinoma

To identify sequences associated with a metastatic phenotype, DNA fragments isolated from 2 separate human colon carcinoma metastases were transfected into a mouse bladder carcinoma cell line together with the neoR gene as selectable marker. It was found that bulk populations of neomycin resistant cells carrying these human sequences caused more metastases in syngeneic mice than did control cells transfected with calf thymus DNA. Cells isolated from metastases retained the highly metastatic phenotype when transferred to secondary hosts.

Oncogene expression in related cancer lines differing in metastatic capacity

Various murine tumor cell lines with different metastatic capacities were tested in vitro for oncogene expression, especially of the p21-Ha-ras protein. Small differences were seen in the expression of several distinct oncogenes in the case of a high metastatic lymphoma variant (ESb) and its low metastatic parental line (Eb). In one instance we observed a 30-fold Ha-ras gene amplification in a metastasis-derived cell line from a spontaneous mouse mammary carcinoma. In spite of this amplification we did not find an increased p21 expression in these cells.

p53 increases experimental metastatic capacity of murine carcinoma cells

Transfection of a cloned p53 gene into a murine bladder carcinoma cell with a low metastatic capacity led to elevated levels of p53 protein in clonal transfectants. After intravenous inoculation into syngeneic mice, p53-transfected clones showed significantly increased metastatic potential in comparison with control transfectants. The observed change did not seem to be due to a change in growth potential per se since the cell lines showed similar growth properties in vitro.

Gene products which play a role in cancer invasion and metastasis

Invasion requires a number of distinct tumor cell interactions with host tissue, beginning with attachment to the matrix, followed by hydrolysis of matrix material and locomotion. Gene products which may be involved in these steps are discussed here. Laminin receptors and integrins have roles in the adhesion phase, while certain collagenases are prominent among the matrix-degrading enzymes. Autocrine motility factors, distinct from growth factors, appear to be involved in tumor cell locomotion. Finally, certain oncogenes, particularly of the ras family, are closely related with metastatic potential. A detailed understanding of the molecular biology of invasion and metastasis could ultimately lead to specific means of interfering with or even reversing these malignant processes.

The ras gene family and human carcinogenesis

It has been well established that specific alterations in members of the ras gene family, H-ras, K-ras and N-ras, can convert them into active oncogenes. These alterations are either point mutations occurring in either codon 12, 13 or 61 or, alternatively, a 5- to 50-fold amplification of the wild-type gene. Activated ras oncogenes have been found in a significant proportion of all tumors but the incidence varies considerably with the tumor type: it is relatively frequent (20-40%) in colorectal cancer and acute myeloid leukemia, but absent or present only rarely in, for example, breast tumors and stomach cancer. No correlation has been found, yet, between the presence of absence of an activated ras gene and the clinical or biological features of the malignancy. The activation of ras oncogenes is only one step in the multistep process of tumor formation. The presence of mutated ras genes in benign polyps of the colon indicates that activation can be an early event, possibly even the initiating event. However, it can also occur later in the course of carcinogenesis to initiate for instance the transition of a benign polyp of the colon into a malignant carcinoma or to convert a primary melanoma into a metastatic tumor. Apparently, the activation of ras genes is not an obligatory event but when it occurs it can contribute to both early and advanced stages of human carcinogenesis.

Restriction fragment length polymorphism analysis and assignment of the metalloproteinases stromelysin and collagenase to the long arm of chromosome 11

Collagenase and stromelysin are two metalloproteinases produced mainly by connective tissue cells and involved in the breakdown of the extracellular matrix. cDNA clones for both of these genes have been isolated and sequencing has shown them to be closely related. The collagenase and stromeylsin cDNA clones have been used to assign these genes to the long arm of chromosome 11 in the regions 11q21-22.1 and 11q22.2-22.3, respectively. This has been achieved using somatic cell hybrids and in situ hybridization. In addition a Taq1 restriction fragment length polymorphism has been demonstrated using the stromelysin cDNA.

Simultaneous transfer of tumorigenic and metastatic phenotypes by transfection with genomic DNA from a human cutaneous squamous cell carcinoma

High-molecular-weight genomic DNA isolated from a human cutaneous squamous cell carcinoma (AS) was assayed for its ability to induce tumorigenic transformation of NIH 3T3 cells. Subcutaneous injection of NIH 3T3 cells cotransfected with DNAs from AS tumor and pSV2-neo plasmid not only induced tumors at the site of injection, but also metastasized spontaneously to the lungs in 100% of nude mice injected. DNA isolated from a representative primary tumor and a metastasis was again used in a second round of transfection. Injection of secondary transfectants into nude mice again resulted in induction of both subcutaneous tumors and spontaneous long metastases. Southern blot hybridization with ras-specific probes revealed that DNA from both primary tumors and metastases induced by AS tumor DNA contained highly amplified Ha-ras oncogene. Furthermore, DNAs from secondary tumors and metastases induced by DNA from a primary tumor and a metastasis also contained similar highly amplified Ha-ras oncogene. These results suggest that the amplified Ha-ras oncogene may be responsible for induction of both tumorigenic and metastatic phenotypes in NIH 3T3 cells transfected with DNA from AS tumor.

In vitro and in vivo regulation of liver epithelial cells carrying a metallothionein-rasT24 fusion gene

We inserted a zinc-responsive metallothionein-rasT24 fusion gene in both orientations into a retroviral vector (SVX) and infected Fisher rat liver epithelial cells. Only the construction in which the viral long terminal repeat and the metallothionein promoters were in opposite orientations resulted in cell lines with biologically altered behavior. Two lines (MTR-1 and MTR-6) showed altered morphology in vitro when ZnSO4 was added to the medium. These cell lines grew in soft agarose in a dose-dependent manner. Immunoprecipitation experiments revealed dose-dependent increases in the rate of synthesis of the mutant p21Ha-ras protein in these lines in response to ZnSO4. Both lines produced poorly differentiated metastatic adenocarcinomas when injected subcutaneously in Fisher rats, and tumors derived from MTR-6 cells grew more rapidly in animals on a zinc-supplemented diet than on a zinc-deficient diet. Uninfected liver epithelial cells showed no change in morphology in vitro after ZnSO4 addition and did not grow in soft agarose or after subcutaneous transplantation during the 14-wk experimental period. These results indicate that altered levels of expression of a single gene (rasT24) can have profound effect on the biologic behavior of tumor cells both in vitro and in vivo.

Transformation by oncogenes encoding protein kinases induces the metastatic phenotype

Oncogenes encoding serine/threonine or tyrosine kinases were introduced into the established rodent fibroblast cell line NIH 3T3 and tested for tumorigenic and metastatic behavior in T cell-deficient nude mice. Transforming oncogenes of the ras family were capable of converting fibroblast cell lines to fully metastatic tumors. Cell lines transformed by the kinase oncogenes mos, raf, src, fes, and fms formed experimental metastases and (in some cases) these genes were more efficient at metastatic conversion than a mutant ras gene. In contrast, cells transformed by either of two nuclear oncogenes, myc or p53, were tumorigenic when injected subcutaneously but were virtually nonmetastatic after intravenous injection. These data demonstrate that, in addition to ras, a structurally divergent group of kinase oncogenes can induce the metastatic phenotype.

A study of mechanisms of carcinogenesis by gene transfer of oncogenes into mammalian cells

Recent work has shown that individual oncogenes can be involved in several steps of the multistage process of carcinogenesis. Evidence comes from studies on the expression of cloned oncogenes transfected into early passage mammalian cells and into immortalized non-tumorigenic cell lines. Transformation of epithelial cells in vitro with cloned cellular and viral oncogenes is of special interest since most human tumors are of epithelial origin. An important aspect of cell transformation by oncogenes is the induction of transforming growth factors (TGFs). The role of oncogenes in differentiation has been examined by introducing the human myc and mutant T24 Ha-ras1 genes into mouse erythroleukemic cells which were then induced to differentiate. In several clones differentiation was inhibited by myc or ras genes. Studies are reported using oncogenes linked to transcriptional control elements that can be regulated in vitro, such as the human metallothionein (hMT-IIA) promoter region, by cadmium and dexamethasone. Phenotypic properties of transfectants including morphological transformation, anchorage dependence and TGF release are shown to be dependent on the regulators of the hMT-IIA control region.

Expression of H-ras correlates with metastatic potential: evidence for direct regulation of the metastatic phenotype in 10T1/2 and NIH 3T3 cells

Using three independent approaches, we studied the effects of H-ras on metastasis formation. Analysis of five in vitro-ras-transfected 10T1/2 clones with either flat or refractile morphologies revealed a relationship between metastatic potential, H-ras expression, and anchorage-independent growth. Four metastatic variants derived from a poorly metastatic, low-H-ras-expressing line all expressed high levels of H-ras RNA and grew efficiently in soft agar. Activation of H-ras expression in the metastatic tumors had occurred through amplification and rearrangement of H-ras sequences. In addition, preinduction of p21 synthesis in NIH 3T3 line 433, which contains v-H-ras under transcriptional control of the glucocorticoid-sensitive mouse mammary tumor virus long terminal repeat, significantly increased metastatic efficiency. Glucocorticoid treatment of normal or pEJ-transformed NIH 3T3 cells did not affect metastatic potential. These data reveal a direct relationship between ras expression and metastasis formation and suggest that metastatic and transformed phenotypes may be coregulated in ras-transformed 10T1/2 and NIH 3T3 cells.

Alteration of the tumorigenic and metastatic properties of neoplastic cells is associated with the process of calcium phosphate-mediated DNA transfection

During the course of studies designed to assess the effect of human Ha-ras gene expression on the malignant behavior of transfected mouse tumor cells we noted that the process of Ca3(PO4)2-mediated DNA transfection was itself associated with profound alterations in tumorigenic or metastatic behavior. The cell line used as a recipient for these studies was a tumorigenic nonmetastatic CBA/J mouse mammary adenocarcinoma line called SP1. When cotransfected with plasmids containing the neo gene (pSV2neo) and the activated Ha-ras gene (pT24-c3), cells from the pooled (5-10 colonies) G418-resistant colonies gave rise to spontaneous lung metastases in 85% of mice after subcutaneous inoculation. However, we noted that 17% of control mice inoculated with G418-resistant pSV2neo-transfected SP1 cells also had lung metastases and that this number approached 100% as the inoculum comprised a greater pool size (50-100 colonies). When cell lines established from isolated pSV2neo-transfected colonies were examined, 3/16 were found to be metastatic. We also found that 3/16 clones grew slowly, or not at all, in CBA/J mice, whereas they grew readily in athymic (nude) mice. The increase in immunogenicity of two out of three of these latter clones was accompanied by expression of the class I H-2Dk major histocompatibility complex antigen that was not detectable in the parental SP1 cells. At least some of these results would appear to be due to exposure to Ca3(PO4)2 alone, as we found that it resulted in 5/20 (25%) clones manifesting metastatic properties. Our results suggest that heritable changes in malignant behavior of transfected tumor cells can be observed at high frequency subsequent to the process of Ca3(PO4)2-mediated DNA transfection, and these changes may be brought about in part by inherited disturbances in expression of recipient cell genes.